PROJECT SUMMARY Inflammatory bowel disease (IBD) constitutes a spectrum of incurable, relapsing and remitting disorders driven by intestinal mucosal barrier function defects and aberrant pro-inflammatory responses directed against microbial flora. IBD patients are at increased risk of developing colitis-associated colorectal cancer (CAC) but the epithelial specific mechanisms that control it are incompletely understood. Also unclear are the genetic factors that predict which IBD patients are likely to progress to CAC. The research focus of this proposal is to uncover how dysregulation of a novel epithelial repair protein, Leucine rich repeat and Ig domain-containing, nogo receptor-interacting protein family 2 (LINGO2) contributes to malignant transformation. In preliminary data, we show that Lingo2 deficiency in epithelial cells results in up-regulation of EGFR phosphorylation, prolonged STAT3 activation in response to IL6 treatment and increased proliferation compared to wildtype cells. Furthermore, Lingo2 deficient mice have severe dextran sodium sulfate (DSS) induced colitis that is rescued by EGFR inhibition. We demonstrate that Lingo2 is expressed in immune cells and its loss in the hematopoietic compartment contributes to susceptibility to colitis. Consistent with the published observations that increased EGFR signaling is pro-tumorigenic, we show that when exposed to azoxymethane (AOM) and DSS, Lingo2 deficient mice are more susceptible to the development of CAC compared to control mice. I therefore hypothesize that Lingo2 protects against the development of CAC through regulation of EGFR and STAT3 activity. The objective is to first mechanistically dissect the cell autonomous role of Lingo2 in epithelial cells in protection from CAC and then to understand whether Lingo2 deficiency in the microenvironment is important for CAC. My hypothesis will be tested through two inter-related Specific Aims that will examine the interplay of LINGO2 and EGFR signaling in epithelial cells in CAC (Aim 1) and then evaluate how Lingo2 deficiency affects the production of STAT3 activating cytokines and activity of myeloid cells in CAC (Aim 2). The experiments proposed will use various innovative approaches including the use of unique knock-in murine models, 3D organoid culture model systems and organoid orthotopic transplantation. The proposed research is significant because it will provide new information about a novel tumor suppressive molecular pathway. University of Pennsylvania provides the perfect research environment to conduct this investigation given local expertise in the inter-related fields of mucosal biology, epithelial biology and immunology. The candidate will gain fundamental skills in murine and in vitro disease modeling and broaden her immunology and epithelial biology knowledge base. These skill sets will greatly enhance the candidate's career development into an independent NIH funded tenure-track faculty member with the long term goal of understanding the mechanisms that control mucosal repair and homeostasis.